1. Field of the Invention
The present invention relates to hemispherical shaped charges. More specifically, it relates to an article comprised of a hemispherical shaped charge with a liner which has a thick wall at its pole and a thin wall at its equator.
2. Description of the Related Art
The structure of most hemispherical shaped charges consists of a case, base plate, charge, and liner. In these shaped charges, the inner and outer surfaces of the liner are spherical or parallel one to the other. The jets produced by these hemispherical charges suffered from major disadvantages; they had jets which had tip velocities which were much lower than those achieved with conical jets.
Following the experience of World War II in which portable anti-tank weapons were developed using explosive charges in various shapes to enhance the armor penetration capacity of such projectiles, it became apparent that shaped charges had potential for use in weapon systems and other areas. The shaped charge came into use as an oil well perforating device for the purpose of enhancing rate of flow in an oil well. The typical shaped charge had a cavity or recess in the forward end of an explosive projectile, and the cavity was typically lined with a dense material such as copper. In use, when the explosive charge was ignited, the detonation wave engaged the metal liner, causing the liner to collapse inwardly upon itself into the cavity. As the collapsing liner reached the center of the cavity, a small forward portion of the liner formed a jet of hot material which was then responsible for the relatively deep penetration achieved in early oil well perforating devices.
The remainder of the collapsed liner formed a large slug of material which followed the advancing energy jet at a lower velocity and contributed little or nothing to penetration. The depth of penetration into the well by the jet depended then, as it does today, on the characteristics of the material of which the liner is made. In general, it is agreed that the liner material for a shaped charge should have a high density and be capable of flowing smoothly into a long jet. Subsequent years of experimentation in this field have brought several developments in an attempt to provide deeper penetration with greater efficiency; however, the full potential of the shaped charge device was not achieved,
While some of these developments have provided small or moderate increases in penetration, little has been recognized of the fundamental scientific principles and the necessary qualities in liner materials and design to transfer the greatest amount of energy from the explosive detonation to the oil well. It is therefore desirable to have a shaped charge that produces a jet with significantly increased stability, coherence, and mass distribution over present designs. The present invention provides such an article.